题目描述 单选 A. ①a[1][1] ②a[1][n] ③a[1][m] ④a[n][m] B. ①a[0][0] ②a[n-1][0] ③a[0][n-1] ④a[n-1][m-1] C. ①a[1][1] ②a[1][m] ③a[n][1] ④a[n][m] D. ①a[0][0] ②a[0][m-1] ③a[n-1][0] ④a[n-1][m-1]